Such a brake apparatus is described by German Patent No. DE-OS 33 38 690. With the apparatus of this prior art, during the braking process which is triggered by activating the brake valve of the tractor vehicle, the brake pressure is increased in the brake mechanism of the trailer vehicle slightly prior to the brake pressure in the tractor vehicle. In this manner, during the braking process, the tractor vehicle and trailer vehicle are kept separated.
The apparatus of the prior art discloses the use of a valve apparatus with two control pistons, connected in series, or a valve having two active surfaces acting on a control piston, which can be controlled in a temporally-staggered manner independently of one another, each with a control circuit with its own pressure medium. The present control circuit, which induces the staggered braking of the trailer vehicle prior to the tractor vehicle, is fed by a pressure medium with a preset and preferably even pressure, so that repeated braking processes can be initiated with uniform effect.
An adaptation to the variable operation of the mechanical control elements of the braking apparatus of the trailer vehicle, as well as a universal application of the valve apparatus of the prior act with different trailer types and manufacturers, each with different mechanical power requirements for the initiation of the braking process, can be accomplished with the apparatus of the prior art only by extensive use of complex means, for example, an adjustable pressure relief valve in the pilot control circuit, downstream of the valve apparatus of the prior art.